He was a high-stakes gambler recognized in the casinos of Nevada. He dabbled in real estate investments in Texas. His last known full-time employment was 30 years ago. He was twice divorced. He had a pilot’s license and had owned two single-engine planes.

While his motive for the mass shooting outside a Las Vegas casino on Sunday night is unknown, details of Stephen Paddock’s history pointed to an unmoored and highly unconventional life.

From his neighbors in a quiet retirement community in Mesquite, Nev., he drew little attention, unless it was for his extreme propensity to keep to himself. He displayed no strong religious or political views, his relatives said, and was not known for angry outbursts.

But he was the son of a bank robber who ultimately escaped from prison and spent most of the 1970s on the F.B.I.’s most wanted list. His girlfriend, sought for questioning by law enforcement officials after the shooting, had passed through Tokyo, officials said.

Details about Mr. Paddock’s career and livelihood were sparse, aside from observations by neighbors and family members that he routinely gambled large amounts of money. “He was a gambler, that was his job,” his brother, Eric Paddock, told reporters Monday at his home in Orlando. “He was a wealthy guy, playing video poker, who went cruising all the time and lived in a hotel room.”

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Stephen Paddock in a photo provided by his brother Eric Paddock.Creditvia Associated Press

Mr. Paddock and his three brothers were raised by their mother, who told the children that their father had died when in fact he was in prison, Eric Paddock said. Mr. Paddock’s father was convicted in 1961 of committing a series of bank robberies, and was sentenced to 20 years, but escaped from La Tuna federal prison in Texas in 1968 and then became a used-car dealer and bingo parlor operator in Oregon.

A “Wanted” poster for the elder Mr. Paddock warned that he was “diagnosed as psychopathic,” “reportedly has suicidal tendencies” and “should be considered armed and very dangerous.”

The children’s mother was left to raise the family on her own. They moved around the country, from Iowa to Tucson to Southern California, another brother, Patrick Paddock II, of Tucson, said. Stephen Paddock’s behavior did not offer any indication of violent tendencies, the brother said.

“He was the least violent in the family during my childhood. So, it’s kind of like, ‘Who?’ ” Comparing himself to his brother, he said, “I have much more anger.”

Stephen Paddock attended college, his family said, and worked for a predecessor company to Lockheed Martin, the aerospace contracting company, from 1985 to 1988. Lockheed Martin confirmed his employment but did not identify the company for which Mr. Paddock worked.

Mr. Paddock once owned and managed a working-class apartment complex in the Dallas suburb of Mesquite, Tex., records show.

He moved away several years ago, she said, and they had not seen each other since. “I thought, it couldn’t be,” she said of the mass shooting. “You would have never thought he would be killing people. You just never know.”

Mr. Paddock bought three guns — a handgun and two rifles — at a shop in Mesquite, Guns & Guitars, within the last year, said Christopher Sullivan, the general manager. All the purchases were legal and cleared routine federal screening, Mr. Sullivan said.

“The man does not have a criminal history,” Mr. Sullivan said.

Two of the gunman’s three brothers said they were not close, and the third could not be located. Patrick Paddock said he and his brother had not been in contact for as long as 20 years, and he did not initially recognize the face that flashed on his television screen. He wondered aloud about the motive behind the crime, and expressed profound distress for the victims.

“My anxiety is not a drop in the ocean compared to how I feel about the people who got killed,” he said.

Eric Paddock broke down in tears during an interview. “There’s nothing I can say. My brother did this. It’s like he shot us. I couldn’t be more dumbfounded,” he said. He said he last communicated with his brother when Stephen inquired about how the family had fared during Hurricane Irma, which struck Florida in September.

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Broken windows at the Mandalay Bay Resort and Casino on Monday.CreditJohn Locher/Associated Press

“He texted me to ask about my mom after the hurricane,” Eric Paddock told reporters. “He sent her a walker.”

He said the situation has been very difficult for their 89-year-old mother, who “had to deal with her husband who was a bank robber, and now this.”

Eric Paddock said that his brother was a wealthy man who gambled for fun. The two brothers had shared a real estate business for decades, refurbishing properties, the sale of which had left his brother with what he estimated was $2 million. “He’s a multimillionaire,” he said. “He helped me become affluent, he made me wealthy.”

She worked as a “high-limit hostess” at the Atlantis Casino in Reno, Nev. from 2010 to 2013, according to her LinkedIn account. On Monday, the casino said that she left the company several years ago. High-limit hostesses attend to members of a loyalty club called Club Paradise who spend large quantities of money and receive discounted hotel rooms, meals and other amenities, according to the casino’s website.

Mr. Paddock seemed to have no criminal history, according to records searches in places where he was known to have lived. The Mesquite Police Department said they had no interactions with the couple, including traffic stops.

Few things seemed out of the ordinary Thursday when Mr. Paddock checked into a suite at the Mandalay Bay Resort in Las Vegas.

But shortly after 10 p.m. Sunday night, from his window on the 32nd floor of the hotel, he unleashed a vicious deluge of bullets from an assault rifle and killed 59 people attending an outdoor country music concert nearby. More than 500 others were injured.

When police stormed his room shortly before midnight, Mr. Paddock lay dead from a self-inflicted gunshot wound. He left behind 23 guns in the hotel suite, including two rifles mounted on tripods, 19 guns in his house, hundreds of rounds of ammunition, broken windows, and a trail of questions by family members and neighbors who are struggling to make sense of his motive. His car remained parked with the hotel valet.

Sheriff Joseph Lombardo of the Las Vegas Metropolitan Police Department described Mr. Paddock as a “lone wolf” whose intentions had gone unnoticed by hotel staff members who had gone in and out of his room without detecting the trove of weapons.

“I can’t get into the mind of a psychopath at this point,” Sheriff Lombardo said.

On Monday, local police had blocked off the entrance to Sun City, the retirement community where Mr. Paddock lived.

Eric Paddock said he and his family were “shocked, horrified” by the news, saying he was “not an avid gun guy.” The brother told CBS News that he knew Mr. Paddock had handguns, but that as far as he knew, Mr. Paddock did not own machine guns.

“Where the hell did he get automatic weapons? He has no military background or anything like that,” the brother said. “When you find out about him, like I said, he’s a guy who lived in a house in Mesquite and drove down and gambled in Las Vegas.”

Eric Paddock told reporters in Florida that his brother “had nothing to do with any political organization, religious organization, no white supremacist, nothing, as far as I know. And I’ve only known him for 57 years.”

Mr. Paddock had a private pilot’s license, according to Federal Aviation Administration, and had two small planes registered in his name.

One of Mr. Paddock’s ex-wives, who now lives near Los Angeles, told the Los Angeles police that they had divorced 27 years ago after being married six years. They had no children.

He owned several homes and properties across the country, according to a review of public records.

“He seemed normal, other than that he lived by gambling,” Sharon Judy, a former neighbor, told Florida Today. “He was very open about that. First time we ever met him, he handed us the key to the house and said, ‘Hey, would you keep an eye on the house, we’re only going to be here every now and then.’ ”

He was a regular at the Eureka Casino Resort in Mesquite, where on Monday the slot machines jangled, the waitresses circled and gamblers folded hundred dollar bills into the hands of eager bookies.

Several people said Mr. Paddock played video poker and card games and had recently won a $20,000 jackpot, a celebrated event at the casino.

“That was his spirit,” said Doug Reath, a Mesquite resident who works in real estate. “He would come here and play.”

A version of this article appears in print on , on Page A1 of the New York edition with the headline: Suspect, an Unmoored Retiree, Kept Quiet and Gambled Often. Order Reprints | Today’s Paper | Subscribe